1. Field of the Invention
This invention relates to a program update system and an electronic device with program update function. More specifically, this invention relates to a system and an electronic device provided with function to update (version up) a control program used to decode compressed data that is taken-in from a USB (Universal Serial Bus) memory or the like.
2. Description of the Related Art
In recent years, an electronic devices such as a car audio takes-in compressed data stored in an external recording medium such as a USB memory or iPod (iPod is a registered trade mark of Apple Incorporated). Standardized audio file formats such as MP3, WMA and AAC are used as a format of the compressed data. The compressed data is decoded by a compression decoder in the electronic device and then played back as a sound through a speaker or the like. At that time, a microcomputer having a USB host function executes a control program of the compression decoder.
In this case, connectability between the electronic device and the USB memory that is available in the market at the time of shipping of the electronic device has been confirmed. That is, the compressed data taken-in from the USB memory is properly decoded by the compression decoder. However, specifications (for example, data output timing) of a USB memory that is released after the shipping of the electronic device may be modified. In that case, there may be caused a problem that the compressed data taken-in from the USB memory released after the shipping of the electronic device is not properly decoded depending on the control program that is installed in the electronic device at the time of the shipping, because the installed control program may not be able to control the compression decoder properly.
Therefore, a flash ROM (an electrically erasable programmable nonvolatile memory, hereafter referred to as an FROM) is incorporated in the electronic device so that the control program is revised using the FROM.
That is, the control program corresponding to the USB memories available in the market at the time of the shipping of the electronic device is written into the FROM in the electronic device. When a new version of USB memory is released after the shipping, update information for the control program is written into the new USB memory. The control program is revised (updated) by writing the update information into the FROM.
Methods to revise the control program of the electronic device are disclosed in Japanese Patent Application Publication Nos. 2006-243997, 2004-151831, 2002-157136 and H09-265391, for example.
In recent years, integrated circuit chips are consolidated into a smaller number of chips in order to reduce a mounting area for them. With the electronic device having the function to update the control program as described above, it is conceivable that the microcomputer having the USB host function, the FROM and the compression decoder are consolidated into a single chip. In this case, however, there is a problem that the single chip has to be manufactured using an FROM process (a manufacturing process required to form the FROM) that increases a manufacturing cost of the single chip.
That is, although the compression decoder and the microcomputer itself, that includes a CPU, a RAM and the like, do not need the FROM process in themselves, they have to be manufactured using the FROM process in order to be integrated in the single chip together with the FROM. However, the FROM process is not suitable for finer design rules required to reduce the size of devices in the single chip, because the FROM process requires a larger number of masks and an increased amount of thermal treatment compared with a logic process that is used to manufacture logic circuits. As a result, the single chip is increased in its die size as well as its manufacturing cost.